Solutions of hydrogen peroxide are utilized for bleaching cellulosic materials, e.g. paper pulps, cotton, linen, jute and the like yarns and woven materials made therefrom. A principal problem is the stabilization of such peroxide solutions during storage prior to and during their use in the above applications. Stabilizers have been used in the past, some of which perform better under acid conditions while others work better under alkaline conditions. Polyphosphates and dipicolinic acid or quinolinic acid will stabilize peroxy solutions in acid media, but not in alkaline solutions, especially those having a pH above 10. Acyltion products of phosphorous acid, e.g. the reaction product with organic acid anhydrides, such as propionic, butyric or caproic anhydrides, or acid chlorides, such as acetyl chloride, have been disclosed as useful in stabilizing H.sub.2 O.sub.2 solutions at pH 10 and above in U.S. Pat. No. 3,122,417. Other phosphonic acid derivatives including amino tri(methylphosphonic acid) and amino tri(ethylidenephosphonic acid) and other like ammonia derived organo phosphonic acids and their salts are disclosed as useful in stabilizing peroxy solutions at alkaline pH conditions in U.S. Pat. No. 3,234,140.
A later patent, U.S. Pat. No. 3,701,825, discloses the use of ethylenediaminetetra(methylenephosphonic acid) and its salts as stabilizers for peroxy-solutions at acid or basic conditions (pH of 1.5 to 13.5). This patent also indicates that the addition of nitrate ion into the solution provides a less corrosive solution.
Bleaching of cellulosic fibers has in the past been conducted with hydrogen peroxide, employing sodium silicate as a stabilizer, but this system results in problems when insoluble silicates are deposited upon the fibers and the machinery employed. When deposited on kraft paper fibers the result is a harsher feel of the paper. The fouling of equipment can cause down-time and shortened life of the equipment. Because of this, silicate-free systems have been suggested.
These silicate-free systems have been found to work well when magnesium salts are preset and, where high amounts of peroxide are employed, the addition of poly-(.alpha.-hydroxyacrylate) as a stabilizer is useful.* The presence of the polyacrylate also improves the brightness (See British Pat. No. 1,425,307). FNT *The use of this stabilizer was discussed in a paper "Hydrogen Peroxide Bleaching of Kraft Pulp and the Role of Stabilization of Hydrogen Peroxide," by G. Papageorges, et al. given at the ESPRA Meeting in Maastricht, Netherlands, May 1979. The British patent gives a method for the preparation of the stabilizer.
In U.S. Pat. No. 3,860,391 the bleaching of cellulose fibers and mixtures of these with synthetic fibers is accomplished by employing peroxide in a silicate-free system in the presence of an aliphatic hydroxy compound, an amino alkylenephosphonic acid compound and, alternatively, with the addition of a polyaminocarboxylic acid. Representative of the above are erythritol or pentaerythritol, ethylene diaminotetra(methylenephosphonic acid) of 1-hydroxypropane-1,1,3-triphosphonic acid and ethylenediaminotetraacetic acid or nitrilotriacetic acid, respectively.
Another patent, U.S. Pat. No. 4,238,282, describes a pulp bleaching system employing chlorine (not peroxide) which uses various chelating agents, including polyacrylic acid (mol. wt.&lt;2000), alkylene polyaminocarboxylic acids, and aminophosphonic acids and their salts.
Other more recent U.S. patents which employ such phosphonates as indicated above, but in a peroxide bleaching system, include U.S. Pat. No. 4,239,643 and U.S. Pat. No. 4,294,575.
While, as noted above, various combinations of chelating agents are useful in stabilizing peroxide bleaching systems, the presence of metal ions, e.g. iron, manganese and copper, provides a catalytic effect with respect to the decomposition of the peroxide and also tends to reduce the brightness of finished mechanical pulps. While the chelants might be expected to take care of minor amounts of the metal ions, the presence of significant amounts of magnesium and/or calcium ions which may be present in the wood pulp or water or both tends to overwhelm the ability of the chelants to complex the iron, manganese and copper ions present.
Certain combinations of the aminephosphonates together with polycarboxylic acids or polycarboxylic amides or a sulfonic acid derivative of a polyamide have now been found to provide stabilization in the presence of significant amounts of magnesium and/or calcium ions and in the presence of small amounts of copper ions and the like which catalyze the peroxide decomposition.